Telegraphone



May 24, 1938. w. c. ELLls Er AL TELEGRAPHONE Filed March 27, 1936 O00- ona coa O00 111111 *lulllfllllnliflfelloL W C .E LL/S B ESGRENER A TTORNEV Y g j @ga g'b f Q7 z a a@ May 24, 1938. w. c. ELLIS Er A1. 2,118,179

TELEGRAPHONE Filed March 27, 193e 2 sheetssheet 2 RECORD/N6 METER wcfLL/s NVENQ/RSESGRf/NER ATTORNEY Patented May 24, 1938 TELEGBAPHONE William C. Ellis, Lynbrook, N. Y., and Earl S. Greiner, East Orange, N. J., aasignors to Bell Telephone laboratories, Incorporated, New York, N. Y., a corporation of New York Application March 27, 1936, Serial No. 71,128

2 Claims. (Cl. 14S- 16) This invention relates to magnetic telegrapoint contains about 3.5 per cent chromium and phones and particularly to an improved record about .8 per cent carbon. member therefor and to a method of treating Th heat treatment comprises heating the tape the member to improve its recording properties. to a suitable temperature in an inert atmosphere,

The object of the invention is to increase the quenching it in an inert atmosphere to a relaefllciency and volume range capacity of telegratively low temperature and maintaining it at the 5 phone systems. quenched temperature for an appreciable time It is well known that when a telegraphone before permitting it t0 return t0 TOOIn temperarecord member is subjected to the action of reture. The treatment is continuous, the tape becording magnets carrying currents representing ing drawn through a furnace and a quenching 10 'Sound Wei/eS. the tape S variously magnetized in head at a suitable speed and from the head its successive elements and that when the tape through teSting deVCeS Which give a Cen'nilOUS so magnetized is passed between suitable reproindication of the volume range of the treated ducing magnetsv connected to a receiver, the origtepe- With thS System the fulnaCe and quench inal sounds are reproduced. ing head temperatures and the tape speed may be 15 Among the qualities which make a magnetic readily adjusted to give best results for the partape or wire suitable for this purpose are a low tiClila-I tape being treatednoise level and the ability to respond to signal The increased volume range of the chrome currents of large amplitude. As the amplitude tape may be utilized to improve a telegraphone of the currents applied to the recording magnets System either by reiSng the level 0f all 0f the 20 is increased, the amplitude of the signal recorded signal components t0 increase the margin bein the tape increases substantially linearly over tween the Signal and the nOSe level 0f the meina considerable range of current amplitudes but ber or by recording signals of a greater range ultimately a point is reached at which norm-ther of amplitudes- It is also found that this tape increase in the signal strength can be obtained. may be magnetized to a given value with a much 25 This maximum value of the signal strength 11x95 lower input level than that necessary for prior the upper limit of the volume range of the tape tapes, which makes it possible to record speech aS a record member. When a. tape having no at apractical level with an efficient carbon microrecorded signal is passed between the magnets phone without the use of an amplifier. of a reproducing system, more or less noise w11) In the drawings Fig. 1 shows furnaces and a 30 be heard. A portion of this noise is due to the quenching head for continuous heat treatment magnetic characteristics of the tape itself and of the tape in accordance with this invention; the level of this inherent noise ilxes the lower 'Flg- 2 ShOWS apparatus 1'01' IneaSiiIing the V01- llmit of the volume range of the tape. It will be urne range of the treated tape: and understood, of course, that in practice the volume Fig. 3 is a series of curves showing the effect 0f 35 range actually used will be slightly less than the quenching temperature on the volume range of maximum value and that the proportion of the the treated tapetotal range used will vary somewhat with the The heat treating furnace H comprises a long requirements of a particular ma Hence for quartz tube I2 around which are woundnresistance purposes of comparisonA with other record memheating elements' and this assembly 1S Suitamy L. bers, it is convenient to speak of the maximum insulated against heat loss by refractory material rather than the useful volumevmnge of member i5 in the steel casing i6. I n order to keep the Heretofore probably the best record membel: temperature of the tape as it leaves the furnace available for such systems was a t to enter the quenching head I1 constant at the ape made by d esired value during the time required for treatilattening carbon steel piano wire which ai'ter i 1 l gms f ta at least two and f 45 suitable heat treatment is capable of recording ng ong en o pe' pre si als ver a nsid bl erably three, independently controllable heating g ,co er e range of amplitude* elements are required. In the furnace shown Applicants haYe found however that chmme the three elements I3, 10, and Il are all energized steel is much Superior to carbo steel for this from a suitable source i8 in accordance with the 50 purpose and when such a chrome steel member is heat-treated according to this invention, it has a volume range morethan 25 'per cent greater than the range oi the carbon steel member. The preferred tape steel from a volume range standsettings of the rheostats 39, 1I, and 40. In addition to these manual controls the elements 10 and ll have automatic recorder controllers 2i! and 2| respectively, which are of the well-known type which intermittently make and break the heat- 55 and curve 62 the total volume range.

ing circuits under the control of the thermocouples 22 and 23 within the furnace to maintain the proper temperature.

The element I3 heats the incoming cold tape to a temperature somewhat below the required quenching temperature, the element 'I0 brings the tape up to very approximately the quenching temperature and the short element It provides any additional heat required to keep the tape leaving the furnace at constant quenching temperature. The quenching head ll has a central tube 25 aligned with the quartz tube i2 of the furnace to form a continuous path for the tape and a jacket 26 surrounding the tube 25 and having an inlet 2l and an outlet 28 for the cooling medium which controls the temperature of the quenching atmosphere in the tube 25.

While the furnace and quenching head are effective in producing a tape which is satisfactory from volume range and noise level standpoints, a tape so treated may be too brittle. A tempering furnace 'It with a single heating element itl and a controlling rheostat 'I may therefore be placed beyond the quenching head to reheat the tape to the temperature necessary to reduce the brittleness to a practical value without impairing its recording properties.

The tape to be treated is drawn from a feed reel 29 through the furnaces and quenching head at a suitable speed by a pulley 30 (Fig. 2) and wound up on the take-up reel 34. The pulley is driven by the motor 3i through the worm gearing 35 and the belt l5 which prevents the vibrations of the driving mechanism from reaching the tape. The reel 34 is connected to the drive through a friction clutch St which is adjusted to keep the tape wound up without subjecting it to excessive tension.

An inert atmosphere in the furnaces and quenching head is provided by feeding a suitable gas, such as nitrogen. under pressure from a tank 3l into the quartz tube i2 at the entrance to the furnace as shown. Excessive leakage is prevented at the furnace entrance by shaping the tube down to give only the necessary clearance for the tape and at the exit end of the tempering furnace by a plug 38.

It will be understood that the optimum tape speed will depend upon various factors such as the thickness of the tape and the lengths of the furnace and of the quenching head. t is found, however, for chrome steel tapes of the order of' l or 2 mils in thickness that the furnace temperature should be from 850 to 1000c C. and that the tape should be quenched for about 7 seconds, In the system shown the furnace I I is about ve feet long, the quenching head is thirty inches long, and the tape is moved at about four inches per second. Circulating steam at C. in the jacket 26 very quickly reduces the temperature of the hot tape and nitrogen from the furnace and maintains it at about 100 C. until it leaves the head. Iiifhe tempering furnace I2 is about three feet long and isoperated at a temperature of about 300 C.

In Fig. 3 curve 60 shows how the highest signal level varies with the temperature from which a 3.5per cent chrome steel tape is quenched, curve 6I the variations in the noise level of the tape These curves are based on a 1000 cycle test frequency recorded on a chrome steel tape .002 inch thick, moving at twelve inches per second with polepieces having tip portions .002 inch thick.

As may be seen from curve Bil-,the volume range of a 3.5 per cent chrome steel tape is of the order of 50 decibels and is not greatly affected by variations in the temperature in the range of 850o C. to 1000 C., but the temperature used has a considerable effect on the stability of the volume range when the tape is stressed by handling and repeated playings. Idler pulleys 63, 6d, and 65 are therefore provided to stress the tape between .the recording and reproducing magnets to an extent at least as great as it is likely to be stressed in ordinary use, so that the volume range indih cated by the meter il will be a more accurate measure of the permanent volume range of the tape. The furnace temperature is then adjusted to give the maximum stable range.

As the treated tape leaves the tempering fui nace it passes successively between polarizing magnets 4I, 4I, the recording magnets lit, @E and the reproducing magnets 43, 43. The polarizing magnets which are energized from the battery 44 bring the tape to a uniformly high magnetization and the battery 45 sets up a depolarizing flux in the magnets t2 to condition the tape to receive a signal as more fully explained in Patent 1,944,238 t0 C. N. Hickman, January 23, 1934.

In this case the signal recorded on the tape is merely for the purpose of testing its volume range capacity and may therefore consist of a single voice frequency such as 400 cycles per second derived from an oscillator 4G. As pointed out above the volume range of the tape is the difference between the noise level and the level of the maxi mum signal which can be recorded. These levels may each be measured continuously but to avoid unnecessary duplication of apparatus they are preferably measured alternately for periods of a few seconds by a recording meter 4'! of the wellknown type which traces a line on a calibrated moving strip. The shaft 49 of the driving pulley 30 also drives the gear 33 and the wheel 50 which has one or more conducting segments 5I for cone necting the brushes 52, 52 together to complete the circuit of the relay 53.

When the relay is unoperated no signal is applied to the tape and the reproducing magnets will deliver to the amplifiers 54, 55 a current representing only the noise inherent in the system. When the relay is operated as shown and the rheostat 50 is properly adjusted, the tape receives its maximum signal from the oscillator I6 and this signal is reproduced by the magnets 43. Due to the very great difference between the noise and signal levels, the resistor 5l in the output of the amplifier 55 is tapped at point 58 for noise meas-- urement and at point 59 for signal measurement and the record strip of the meter 4l is preferably calibrated so that the noise and signal levels and the volume'range can be read directly from the meter.

While the invention has been described with particular reference to 3.5 per cent chrome steel tape it will be understood that the apparatus and general method are also applicable to the heat treatment of other tapes and since the testing apparatus gives an immediate and continuous check on the volume range being obtained, the tape speed and furnace temperatures may be easily changed to suit the ycharacteristics of any other tape.

What ls claimed is:

1. The method of heat treating telegraphonrecord members which comprises drawing the .member through an inert atmosphere of high temperature into and through en ..sm.-.

stressed by bending before the signal isreproduced, to nn extent It least u great u thnt produced by the normni use oi the member in n telegrnpbone machine no that the volume ruige indicated will be the permanent volume range ol 5 the member.

WILLIAM C. ELLIS. EARL B. GRIINIR. 

